ANGIOTENSIN-II RECEPTOR-TYPE I-REGULATED ANION SECRETION IN CYSTIC-FIBROSIS PANCREATIC DUCT CELLS

The beta-adrenergic (cAMP-dependent) regulation of Cl- conductance is defective in cystic fibrosis (CF). The present study explored alternat ive regulation of anion secretion in CF pancreatic ductal cells (CFPAC -1) by angiotensin II (AII) using the short-circuit current (I-SC tech nique. An increase in I-SC could be induced in CFPAC-1 cells by basola teral or apical application of AII in a concentration-dependent manner (EC(50) at 3 mu M and 100 mM, respectively). Angiotensin receptor sub types were identified using specific antagonists, losartan and PD12317 7, for AT(1) and AT(2) receptors, respectively. It was found that losa rtan (1 mu M) could completely inhibit the AII-induced I-SC whereas, P D123177 exerted insignificant effect on the I-SC indicating predominan t involvement of AT, receptors. The presence of AT(1) receptors in CFP AC-1 cells was also demonstrated by immunohistochemical studies using specific antibodies against AT(1) receptors. Confocal microscopic stud y demonstrated a rise in intracellular Ca2+ upon stimulation by AII in dicating a role of intracellular Ca2+ in mediating the AII response. D epletion of intracellular but not extracellular pool of Ca2+ diminishe d the AII-induced I-SC. Treatment of the monolayers with a Cl- channel blocker, DIDS, markedly reduced the I-SC indicating that a large port ion of the AII-activated I-SC was Cl--dependent. AII-induced I-SC was also observed in monolayers whose basolateral membranes had been perme abilized by nystatin, suggesting that the I-SC was mediated by apical Cl- channels. Our study indicates an AT(1)-mediated Ca2+-dependent reg ulatory mechanism for anion secretion in CF pancreatic duct cells whic h may be important for the physiology and pathophysiology of the pancr eas.